1. Laboratory Animal Research Center; Minato-k Tokyo 108
2. Department of Pathology, Institute of Medical Science; The University of Tokyo; Minato-ku Tokyo 108
3. Department of Pathology; Hokkaido University School of Medicine; Sapporo, Hokkaido 060
4. Department of Neurological Virus Disease, Institute for Virus Research; Kyoto University; Sakyo-ku, Kyoto Kyoto 606